Psychophysiological mechanisms of panic attacks have not yet been clarified. Two current points of view exist. One proposes that panic patients experience specific and significant physiological changes (i.e. increases in blood pressure, heart rate and respiratory rate). Another theory says that panic patients are highly sensitive to even small changes in their physiological parameters. However, there has been very little empirical research data confirming these theories. The aim of this study is to investigate panic patients' abilities to sense and to discriminate changes in their physiological parameters, specifically, their heart rate, respiratory rate and blood pressure. At the same time we will examine the magnitude and nature of physiological changes in these patients. This will be done by using the technique of computer-aided continuous monitoring of anxiety self- reports, which allows us to simultaneously record the patients' self- reports of anxiety along with their psychophysiological parameters (i.e. heart rate, blood pressure, GSR, electromyogram, and respiratory rate). Using this technique we will examine and compare correlations between the self-reports of anxiety and the physiological changes in panic patients and in normal subjects. This will be done under three conditions: at rest, during inhalation of carbon dioxide and after inhalation of carbon dioxide. We will also examine panic disorder patients' ability to estimate changes in their systolic blood pressure and heat rate, and then compare their data to those of the normal subjects. This will also be done during the rest period, during the provocation of panic attack by inhalation of carbon dioxide and during the period of recovery after the carbon dioxide inhalation. This study will increase our insight into psychophysiological mechanisms of this condition. It may also assist and will improve our understanding of this condition. It may also assist us in finding new ways of treating panic disorders.